At present, the most effective method for examination of body cavities in human patients is by endoscopes. For examination of the air passages of the lung, a flexible endoscope is usually used, commonly referred to as a bronchoscope. Bronchoscopes, like all endoscopes, employ visible white light to illuminate the surface under examination. The illuminating light is brought into the air passages (bronchi) of the lungs via a fiberoptic illuminating light guide. The reflected and scattered light from the bronchial tissues is captured by a projection lens which focuses the image into the bronchoscope's imaging bundle. The imaging bundle is composed of several thousand individually wrapped fibers, which transmit a coherent image to the exterior of the body. This image is then projected through the ocular of the bronchoscope for human observation. A colour video camera can be attached to the eyepiece of the bronchoscope such that colour images of scattered/reflected white (broadband) light can be viewed on a colour video monitor.
Using a conventional bronchoscope, large invasive cancers can be readily seen. However, focal inflammation, denudation, dysplasia, and early lung cancers cannot be readily seen by such an apparatus.
Several methods have been developed to visualize small early lung cancers which are difficult to detect by ordinary white light bronchoscopy. All of these involve the use of tumour localizing drugs, e.g. Haematoporphyrin derivatives or Porfimer sodium, which have been shown to be preferentially retained in tumour tissues. Some of these drugs also fluoresce and their fluorescence can be detected by non-imaging and imaging devices (Profio AE et al., Med Phys 6:532-535, 1979; Prorio AE et al., Med Phys 11:516-520, 1984; Profio AE et al., Med Phys 13:717-721, 1986; Hayata Y et al., Chest 82:10-14, 1982; Kato A, Cortese DA, Clin Chest Med 6:237-253, 1985; Montan Set al., Opt Letters 10:56-58, 1985). The drawback of these techniques is the use of drugs which may have serious side effects and therefore may not be appropriate for diagnostic purposes. In addition, the use of non-imaging devices such as the ratio fluorometer probe (Profio et al., Med. Phys 11:516-520, 1984) cannot delineate the exact site and dimensions of the abnormal areas.
An alternative approach for detecting invasive tumours has been proposed by Alfano et al in U.S. Pat. No. 4,930,516 issued Jun. 5, 1990. Alfano discloses a method of detecting cancers on the basis that the fluorescence spectra of cancerous tissues is different from normal tissues in that the maximal fluorescence peak of tumour tissues is blue shifted to lower wavelengths (from 531 nm to 521 nm). These observations were made based on in vitro measurements in excised, large (invasive) animal and human tumours but have not been reported on human tumours in vivo. In addition, there are no reports of other abnormal tissues such as inflamed or pre-cancerous tissues. We have measured tissue autofluorescence in human patients in vivo using different excitation wavelengths including 405 nm, 442 nm, and 488 nm by a specially designed optical multichannel analyzer which can be attached to a conventional bronchoscope. Contrary to the observation by Alfano et al., we did not find any difference in the shape of the fluorescence spectrum between normal and tumour tissues using these excitation wavelengths. In particular, there was no blue shift of the emission peaks. We observed a significant difference in the overall fluorescence intensity especially in the green region of the visible spectrum. A significant but a lesser decrease in the overall fluorescence intensity was also found in precancerous and non-cancerous lesions (dysplasia and metaplasia).
The decreased green fluorescence may be attributed to a reduced level of oxidized form of riboflavin. Riboflavin emits strongly in the green region and is believed to be predominantly responsible for the strong green fluorescence in normal human lung tissue. In the cancerous tissues, much less riboflavin was found (Pollack MA et al., Cancer Res 2:739-743, 1942) and/or is present in the reduced state. This may account for the reduced autofluorescence in premalignant and malignant bronchial tissues.
Tests were conducted revealing examples of such decreased tissue autofluorescence for dysplastic bronchial tissue, and carcinoma in situ. It was determined that the main difference between abnormal and normal tissues is manifested by a greatly reduced fluorescence intensity in the region of the spectrum from 480 nm-600 nm. At wavelengths greater than approximately 635 nm, the tissue autofluorescence is approximately the same between abnormal and normal tissues. Test were conducted using excitation light of 442 nm, 405 nm and 488 nm and abnormal tissue results were compared to normal tissue results. All of these data were obtained in vivo during standard fiberoptic bronchoscopy using the optical multichannel analyzer.
Because of the observed large decrease in the emitted fluorescence without a change in the spectral profile in the abnormal tissues, methods using ratioing of two or more wavelengths that was originally described by Profio and coworkers and then studied in patients who have received fluorescent drugs such as Photofrin (Profio et al., Med. Phys. 11:516-520, 1984) generally will not differentiate abnormal from normal bronchial tissues using autofluorescence alone.
We have invented and constructed an apparatus which exploits differences in autofluorescence intensity for the detection and delineation of the extent of abnormal areas in the human body, particularly the lung.